1. Field of the Invention
The present invention relates to a transmission path interface apparatus for interfacing between an information terminal giving transmission information to be sent and a transmission path compatible to a carrier sense multiple access (CSMA) mode or carrier sense multiple access with collision detection (CSMA/CD) mode and matching the transmission mode of the transmission path and the transmission information.
In the CSMA/CD mode, access to the transmission path is achieved under communication controls distributed to individual nodes. This enables simplification and standardization of the configuration of the hardware in a flexible manner and reduces the possibility of the spread of a failure occurring in any node to the other nodes, therefore has been frequently applied to bus like local area networks (LANs).
Further, in recent years, in addition to the technologies for prevention and correction of transmission error, digital modulation and demodulation technology compatible with these techniques have been established, therefore wireless LANs using not only radio waves, but also infrared rays etc. as carriers have been commercialized and are spreading as core elements of office automation systems.
2. Description of the Related Art
As will be explained in detail later by using the drawings, in a wireless LAN of the related art comprised of a master station, a wireless transmission path, a plurality of slave stations connected to the master station via the wireless transmission path, and personal computers coupled to the slave stations, when wireless packets are sent by a plurality of slave stations in parallel to an uplink of the wireless transmission path, the master station cannot normally receive the wireless preambles contained in part or all of these wireless packets. For this reason, no loopback signals corresponding to the related wireless packets are sent to a downlink of the wireless transmission path.
In such a case, any of the plurality of personal computers which is standing by for confirming the loopback signal must suspend transmission of the following identification information and transmission information over an interval T mentioned later. In this case, the interval T generally becomes longer than a sum of the time required for the processing to be carried out in the master station and the time required for propagation in the uplink and downlink of the wireless transmission path and becomes a value equal to or longer than a time corresponding to the maximum length of the wireless packet. Therefore, the possibility of reduction of the transmission efficiency was high.
Further, the transmission efficiency is more conspicuously lowered the larger the number of slave stations attempting to send wireless packets in parallel on uplinks of the wireless transmission path, therefore technology capable of maintaining the transmission efficiency high even if the number of slave stations is increased is in demand.
Therefore, an object of the present invention is to provide a transmission path interface apparatus capable of identifying at a high speed and with a high accuracy that the loopback signal cannot be given.
To attain the above object, a transmission path interface apparatus according to the present invention is constituted by providing a transmitting means for holding serial transmission information and transmitting a frame modulated by both the transmission information and a preamble to a CSMA mode transmission path; a receiving means for taking out a loopback frame transmitted by an opposing node in accordance with that frame, restoring the transmission information contained in this, and holding the same; a collision decision means for determining a correlation between transmission information held by the transmitting means and the receiving means and notifying a result of this to a source of transmission information; and a collision decision accelerating means for comparing an elapsed time from a timing when the information source gave the transmission information to the transmitting means to a timing when the transmission information contained in the loopback frame is restored with a threshold value indicating the maximum time of a delay allowed with respect to the transmission of the frame containing the following transmission information and giving notification that the former exceeds the latter to this information source.
By this, a transmission path interface apparatus compatible with the CSMA mode capable of responding to a failure occurring in the transmission path flexibly and at a high speed is realized.